There’s no need to explain this, isn’t it? Okay as it is, this is to deny someone’s utterance. But don’t take it so logically, please. If you don’t really really want to believe it, if you really get upset, you just take a deep breath and shout 嘘だッ！[usodaaaa!] to mean “THAT IS NOT TRUE!.” So you can triumph over him/her for sure.
See? This stems from the famous doujin game, ひぐらしのなく頃に[When They Cry]. Particulary the lead heroine Ryugu Rena says this when she gets upset all of a sudden. Rena is usually such a cute merry girl, and loves to collect adorable stuff. But you can’t anticipate when she gets upset, so that when the time comes, you would be terrorized for sure. Since she acts so scary when she shouts 嘘だッ！, this has become famous among not only Higurashi fans but any other anime fans…even 2ch. There is even a community named 嘘だッ！on mixi! I wonder what they are doing…
At any rate, you can use this from now. For example, when you have a chat with your friend, instead of saying “You’ve got to be kidding!,” say 嘘だッ！Make sure you stay cool until you say this because this doesn’t work unless you get upset all of a sudden.
Then I shall tell you my experience. When the certain Singaporean friend of mine came to Tokyo, we met up and had a chat. He mentioned an adult’s toy named Tenga which functions as a woman’s sexual organ. He insisted he bought it as a souvenir and never tried it out.
a. So did you try it out? [使ったんでしょ？]
b. No I haven’t. [使ってないよ。]
a. Are you sure? [本当に？]
b. Y-Yeah. [う、うん。]
a. Why are you lying? Huh? [どうして嘘つくのかな、カナ？]
b. I am not lying… [嘘じゃないよ…]
So I said…
In the end, he admitted he actually usMake 嘘だッ！your own language! ^^
That’s all for today, good-bye～♪